Known methods of introducing additives to polymeric particles include dry blending the materials, melting, and compounding the melted blend with extruders and pelletizing or powdering to the desired physical form. The additives include antioxidants, processing aids, slip agents, antiblocking agents, antistatic agents, lubricants, UV stabilizers, coupling agents and colorants.
Another method of introducing additives to polymeric particles is at the extruder hopper during end use processing. Additives such as colorants, slip agents, processing aids, blowing agents, and others are introduced to virgin polymeric particles at this stage usually in concentrate form. In many instances, difficulty is encountered in metering the exact amounts necessary to do a specific job. This is especially true for additives such as processing aids and external lubricants which are used at very low levels and usually cannot be added in a concentrate form.